Angular velocity sensor and angular velocity detector

ABSTRACT

The present invention provides a cheap angular velocity sensor capable of detecting angular velocity with high precision by using a vibrational mode which cannot be obtained by external vibration. The angular velocity sensor includes: a vibrator ( 2 ) made of a magnetostrictive material; a first coil ( 4 ) disposed along a first plane which includes an axis (A) of the vibrator ( 2 ), the first coil enclosing the vibrator; a supporter supporting the vibrator ( 2 ) at a position where the axis (A) crosses the surface of the vibrator ( 2 ), the supporter made of a nonmagnetic material; and a second coil ( 6 ) disposed along a second plane which crosses the first plane and includes the axis (A), the second coil enclosing the vibrator ( 2 ) and the first coil ( 4 ). The first coil ( 4 ) generates a magnetic field in the vibrator ( 2 ) on the basis of an excitation current supplied, thereby making the vibrator ( 2 ) vibrate in the direction of the magnetic field, and the second coil ( 6 ) detects a magnetic flux change caused by a change in the vibration of the vibrator ( 2 ), the change in the vibration occurring depending on angular velocity.

TECHNICAL FIELD

The present invention relates to an angular velocity sensor using avibrator made of a magnetostrictive material and to an angular velocitydetector using the angular velocity sensor.

BACKGROUND ART

To detect angular velocity, various methods are practically usedconventionally. Among them, as an angular velocity sensor having arelatively simple structure and, moreover, which is cheap, there is awidely used angular velocity sensor employing a method of detectingangular velocity by detecting, by some method, a Coriolis forcegenerated in the direction orthogonal to the vibration direction whenthe angular velocity is applied to the vibrator in a one-dimensionalvibration motion state. The angular velocity sensor is called a rategyro. In particular, the angular velocity sensor using the vibrator isgenerally called a vibration gyro. In the vibration gyro, in many cases,a vibration member is made by using piezoelectric ceramics and, whenangular velocity is applied to the vibration member vibrated by applyingAC voltage, a displacement which occurs in the vibrator by the Coriolisforce is extracted as an electric signal by the piezoelectric effect,and angular velocity is detected.

However, the piezoelectric angular velocity sensor using thepiezoelectric ceramics has the following problems. Specifically, theangular velocity sensor has to employ either the configuration ofadhering a piezoelectric element to a vibrator or the configuration ofusing a piezoelectric element as the vibrator itself. In any of thecases employed, to drive the piezoelectric element and detect anelectric signal by the piezoelectric effect, a wire has to be connectedto an electrode of the piezoelectric element. As a result, externalvibration is transmitted to the vibrator via the wire, and a problemoccurs such that the angular velocity cannot be detected accurately.

To solve the problem, for example, in a vibration gyro (10) described inJapanese Patent Laid-open No. Hei 5-1917, as shown in FIG. 1 of thepublication, a vibrator (12) is supported by supporters (22a and 22b)attached near a node point. As shown in FIG. 2 in the publication, leadwires (24a and 24b) are wound around the supporter 22b along thevibrator (12). Further, the lead wires (24a and 24b) are attached to thevibrator (12) by an elastic adhesive (26) such as silicone from thesupporter (22b) to a portion near piezoelectric elements (14a, 14b).Similarly, a lead wire (24c) is partially adhered to the elasticadhesive (26) along the vibrator (12) and is wound around the supporter(22a). With the configuration, in the vibration gyro (10), the leadwires (24a to 24c) are attached to the vibrator (12) by using theelastic adhesive (26), so that the elastic adhesive (26) functions as adumping material. Therefore, external vibration transmitted to the leadwires (24a to 24c) is damped (reduced) and, as a result, the influenceof the external vibration on vending mode vibration of the vibrator (12)is lessened.

In the vibration gyro (10), however, since the dumping characteristicchanges according to the amount of the elastic adhesive (26), it isdifficult to make the degree of lessening the external vibrationconstant (reproducibility is not excellent). Consequently, a problemexists such that it is difficult to detect the angular velocity withhigh precision. The elastic characteristic of the elastic adhesive (26)changes (deteriorates) due to temperature change or change with time.Therefore, the vibration gyro (10) also has a problem that it isdifficult to excellently reduce leakage of vibration for long period. Itis not easy to manage the elastic adhesive (26) and, moreover,workability of the elastic adhesive (26) is low. There is consequently aproblem that it is also difficult to improve productivity of thevibration gyro (10).

As a method capable of more effectively reducing the influence on thevibrator of external vibration, a vibration gyro in which the vibratoris vibrated in a vibrational mode which is hardly set for the vibratorby the external vibration is proposed. As a vibration gyro of this kind,for example, a gyro (gyroscope) disclosed in Japanese Patent Laid-openNo. Hei 10-267667 is known. In this gyro, a ring-shaped vibrationresonator (1) is suspended in magnetostaic field by a plurality offlexible supporting beams (5), and a vibrational mode of vibrating thevibration resonator (1) by electromagnetic induction so that the shapecan be changed from a ring shape to an oval shape or from the oval shapeto the ring shape is used. Since the vibrational mode is hardly set byexternal vibration, in the structure, even when external vibration isadded, the influence on the vibrational mode is extremely small.Therefore, in the gyro, also in the case where the external vibration isadded, the angular velocity can be detected with precision.

The gyro has a problem that the plurality of flexible supporting beams(5) supporting the vibration resonator (1) have to be manufactured withhigh precision by using, for example, micromachining, so that themanufacturing cost is high.

On the other hand, in the angular velocity sensor disclosed JapanesePatent Lid-open No. Hei 7-20140, excitation generated by a drive coil(12) is given to a vibrator (11) made of a magnetostrictive material,thereby generating vending mode vibration. When angular velocity isadded to the vibrator (11) in the vibration state, the Coriolis force inthe direction orthogonal to the vibration direction is generated in aleg portion of the vibrator (11). In this case, the vibration directionis slightly shifted (twisted) from the basic vibration direction by theCoriolis force. As a result, a stress acting on the leg portion changes,and magnetization caused by an inverse magnetostriction also changes.Consequently, in the angular velocity sensor, by detecting a change inthe magnetization by detection coils (13a and 13b), the angular velocityapplied to the vibrator (11) can be detected in a non-contact manner.

However, since the vibrational mode used in the angular velocity sensor(the vibrational mode of making the vibrator (11) vending mode vibrate)is a vibrational mode which is easily influenced by external vibration,the angular velocity sensor has a problem that it is difficult to detectthe angular velocity with high precision.

As described above, conventionally, various angular velocity sensorshave been developed. As described above, in the angular velocity sensorsdisclosed in Japanese Patent Laid-open Nos. Hei 5-1917 and Hei 7-20140,since the vibrator is easily influenced by the external vibration, aproblem that it is difficult to detect the angular velocity with highprecision exists. In the gyro disclosed in Japanese Patent Laid-open No.Hei 10-267667, although the influence of external vibration on thevibrator can be reduced, the problem such that the manufacturing costbecomes very high.

DISCLOSURE OF THE INVENTION

The present invention has been achieved in consideration of the problemsand an object of the invention is to provide a cheap angular velocitysensor and angular velocity detector capable of detecting angularvelocity with high precision by using a vibrational mode which cannot beset by external vibration.

An angular velocity sensor according to the present invention includes:a vibrator made of a magnetostrictive material in a disc shape in planview; a first coil disposed along a first plane which includes an axisof the vibrator, the first coil enclosing the vibrator; a supportersupporting the vibrator at a position where the axis crosses the surfaceof the vibrator, the supporter made of a nonmagnetic material; and asecond coil disposed along a second plane which crosses the first planeand includes the axis, the second coil enclosing the vibrator and thefirst coil. One of the first and second coils generates a magnetic fieldin the vibrator on the basis of an excitation current supplied, therebymaking the vibrator vibrate in the direction of the magnetic field, andthe other one of the first and second coils detects a magnetic fluxchange caused by a change in the vibration of the vibrator, the changein the vibration occurring depending on angular velocity.

Preferably, the angular velocity sensor has a case made of a magneticmaterial for housing the vibrator, the first coil, and the second coil.

A first angular velocity detector according to the invention isconfigured by disposing the angular velocity sensor described above oneach of two axes orthogonal to each other.

A second angular velocity detector according to the invention isconfigured by disposing the angular velocity sensor described above oneach of three axes orthogonal to each other.

As described above, in the angular velocity sensor according to theinvention, one of the first and second coils generates a magnetic fieldin the vibrator on the basis of an excitation current supplied, therebymaking the vibrator vibrate in the direction of the magnetic field, andthe other one of the first and second coils detects a magnetic fluxchange caused by a change in the vibration of the vibrator, which occursdepending on angular velocity. In such a manner, the vibrator can bevibrated in the vibration state (vibrational mode) which cannot be setin a normal state. Thus, while avoiding inhibition of vibration to thevibrator by the supporter, even when external vibration is transmittedto the vibrator, the vibrator can be maintained in a vibration state inthe basic vibration almost without an influence of the externalvibration. Therefore, the angular velocity sensor can detect the angularvelocity with high precision also in a state where the externalvibration is applied. By employing the simple configuration ofsupporting the vibrator only by the supporter, the angular velocitysensor can be manufactured at sufficiently low cost.

In the angular velocity sensor according to the invention, by housingthe vibrator, the first coil, and the second coil in the case made ofmagnetic material, leakage to the outside of the case of the magneticfield generated by one of the first and second coils can be prevented,and invasion of external magnetic field to the inside of the case issuppressed, thereby enabling the influence of the external magneticfield on the vibrator and the other one of the first and second coils tobe reduced. Since the case configures a closed magnetic path for themagnetic field generated by one of the coils together with the vibrator,leakage magnetic flux can be reduced and, as a result, the vibrator canbe vibrated more efficiently.

In an angular velocity detector according to the invention, the angularvelocity sensor is disposed on each of two or three axes orthogonal toeach other. Consequently, even in a state where external vibration isapplied, the angular velocity in the two or three axes can be detectedwith high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an angular velocity sensoraccording to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an internal structure ofthe angular velocity sensor, an oscillation driving circuit, and asynchronous detector.

FIG. 3 is a plan view of a vibrator, an excitation coil, and a detectioncoil, indicating the direction of a combined magnetic field generated bythe excitation coil, and the vibration direction of the vibrator in astate where no angular velocity is added to the angular velocity sensor.

FIG. 4 is a plan view of the vibrator, the excitation coil, and thedetection coil, indicating the direction of a magnetic field in thevibrator and the vibration direction of the vibrator in a state whereclockwise angular velocity is added to the angular velocity sensor.

FIG. 5 is a plan view of the vibrator, the excitation coil, and thedetection coil, indicating the direction of a magnetic field in thevibrator and the vibration direction of the vibrator in a state wherecounterclockwise angular velocity is added to the angular velocitysensor.

FIG. 6 is an exploded perspective view showing the configuration of anangular velocity detector using three angular velocity sensors.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of an angular velocity sensor and an angularvelocity detector according to the present invention will be describedhereinbelow by referring to the attached drawings.

First, the configuration of an angular velocity sensor according to theinvention will be described with reference to the drawings.

An angular velocity sensor 1 has, as shown in FIGS. 1 and 2, a vibrator2, a supporter 3, a first coil 4, an oscillation driving circuit 5, asecond coil 6, a synchronous detector 7, and a case 8. In theembodiment, as an example, the first coil 4 is used as an excitationcoil, and the second coil 6 is used as a detection coil. Consequently,the first coil 4 is also called an excitation coil 4, and the secondcoil 6 is also called a detection coil 6.

In this case, as shown in FIG. 3, the vibrator 2 is formed in a discshape in plan view (as an example, a flat disc member) by using amagnetostrictive material having a positive magnetostrictioncharacteristic which extends irrespective of the direction of a magneticfield applied. In this case, as the magnetostrictive material, amaterial having a positive or negative magnetostriction characteristic,concretely, an Ni—Fe-base magnetostrictive material, an RFe-basemagnetostrictive material, or the like can be used. As themagnetostrictive material, an isotropic magnetostrictive material whosedirection indicative of the magnetostriction effect is random is used.To increase the efficiency of vibration in the vibrator 2, it ispreferable to use an anisotropic magnetostrictive material whosedirection is aligned with that of a magnetic field applied. In the caseof using the anisotropic magnetostrictive material, the vibrator 2 isdisposed in the direction along the direction of the arrow B orthogonalto a first plane PL1 in which the axis A (refer to FIG. 3) passes andthe first coil 4 is disposed in the surface of the vibrator 2.

The supporter 3 is formed in a cylindrical shape as an example by usinga nonmagnetic material. As shown in FIG. 2, one end face (under face) ofthe supporter 3 is fixed to the upper face of the lower frame of abobbin 11 which will be described later in the first coil 4, the otherend face (top face) of the supporter 3 is fixed to the center portion ofthe under face of the vibrator 2 (portion where the axis A passes in thesurface of the vibrator 2) in a state where the axis of the supporter 3and the axis A of the vibrator 2 coincide with each other and, whileavoiding contact between the first and second coils 4 and 6, thevibrator 2 is supported. In this case, the center portion of the underface of the vibrator 2 functions as a center point (fixed point) ofvibration by the vibrator 2. The fixed point has the property that evenwhen magnitude or direction of the angular velocity applied to theangular velocity sensor 1 changes, the function as the center ofvibration does not change. Therefore, without being influenced byvibration applied from the outside, accurate angular velocity detectioncan be performed in a wide angular velocity area.

As shown in FIGS. 1 and 2, the excitation coil 4 is formed by winding awire (for example, covered copper wire) around the outer peripheral faceof the bobbin 11 made of a nonmagnetic material (for example, asynthetic resin) formed in a frame shape having a rectangular shape inplan view. The excitation coil 4 is disposed so as to enclose thevibrator 2 on the first plane PL1 (refer to FIG. 3) including the axis Aof the vibrator 2. The excitation coil 4 makes the vibrator 2 vibrate byapplying to the vibrator 2 a magnetic field generated on the basis of adrive signal Sa supplied from the oscillation driving circuit 5.

As shown in FIG. 2, the oscillation driving circuit 5 generates thedrive signal Sa and a reference signal Sb synchronously with the drivesignal Sa, supplies the drive signal Sa to the excitation coil 4, andsupplies the reference signal Sb to the synchronous detector 7. As anexample, the oscillation driving circuit 5 generates, as the drivesignal Sa, a signal obtained by superimposing DC voltage for applyingthe bias magnetic field to the vibrator 2 with AC voltage. Therefore,the vibrator 2 can be efficiently made vibrate in an area wherelinearity is high and a change amount is large.

As shown in FIGS. 1 and 2, the detection coil 6 is formed by winding awire (for example, covered copper wire) around the outer peripheral faceof a bobbin 12 made of a nonmagnetic material (for example, a syntheticresin) formed in a frame shape having a rectangular shape in plan view.The detection coil 6 is disposed so as to enclose the vibrator 2 and theexcitation coil 4 on a second plane PL2 (refer to FIG. 3) crossing (inthis example, orthogonal to) the first plane PL1 and including the axisA. As shown in FIG. 3, the detection coil 6 is disposed so as to beorthogonal to the excitation coil 4 in plan view. As mentioned below,the detection coil 6 detects an induced voltage according to the numberof magnetic fluxes passing through (penetrating) the inside of thedetection coil 6 among magnetic fluxes generated by the excitation coil4.

The synchronous detector 7 synchronous-detects a signal Sc induced atboth ends of the detection coil 6 by the voltage according to the numberof magnetic fluxes passing through the detection coil 6 with thereference signal Sb, and outputs a DC detection voltage Vd having avoltage value according to the voltage value of the signal Sc and havingthe polarity (positive or negative) according the phase of the signalSc.

The case 8 has, as shown in FIGS. 1 and 2, an upper case 21 and a lowercase 22 each made of a magnetic material. In this case, the upper case21 is formed in a cylindrical body whose one end (upper end in thediagrams) is closed and the lower end is opened. The diameter (insidediameter) of the upper case 21 is slightly larger than the length in thelongitudinal direction in the excitation coil 4 and the detection coil 6so that the members and the vibrator 2 can be housed. On the other hand,the lower case 22 is formed in a disc member capable of closing the openside (lower end side in the diagram) of the upper case 21, and functionsas a cover for the upper case 21 and a stand on which the excitationcoil 4 and the detection coil 6 are placed. As an example, the lowercase 22 is configured as a disc member with a step which can be fit inthe upper case 21, and whose center portion on the face on the uppercase 21 side is formed in a cylindrical shape which can be fit in theupper case 21. With the configuration, in a state where the open side ofthe upper case 21 is closed with the lower case 22, relative positionaldeviation between the upper and lower cases 21 and 22 is prevented. Onthe upper surface of the center portion in the lower case 22, a pair ofsupporting stands 23 made of a nonmagnetic material for supporting theexcitation coil 4 is disposed.

The detection coil 6 is placed on the top face of the center portion inthe lower case 22 in the case 8 having such a configuration, and theexcitation coil 4 is placed on the supporting stands 23 and 23 so thatthe axis A of the vibrator 2 and the axis of the case 8 coincide witheach other, thereby housing the coils 4 and 6 and the vibrator 2supported by the supporter 3 in the case 8. Therefore, the upper andlower cases 21 and 22 made of a magnetic material has a shield functionof reducing the influence of the external magnetic field on the vibrator2 and the detection coil 6 by preventing leakage of the magnetic fieldgenerated by the excitation coil 4 to the outside of the case 8 andsuppressing invasion to the inside of the case 8 of the externalmagnetic field. The case 8 further has the function of forming a closedmagnetic path for the magnetic field generated by the excitation coil 4together with the vibrator 2.

The angular velocity detecting operation of the angular velocity sensor1 will now be described with reference to the FIGS. 2 to 5.

In a state where the drive signal Sa is supplied from the oscillationdriving circuit 5 to the excitation coil 4, as shown in FIG. 3, theexcitation coil 4 generates a combined magnetic field C passing throughthe area where the vibrator 2 is disposed. In this case, the combinedmagnetic field C is generated by combining a bias magnetic field basedon the DC voltage in the drive signal Sa and an alternating field basedon the AC voltage in the drive signal Sa. Since the combined magneticfield C passes through a magnetic circuit (closed magnetic path) formedby the vibrator 2 and the upper case 21 disposed so as to surround thevibrator 2, the combined magnetic field C is efficiently supplied to thevibrator 2. The direction of the combined magnetic field C coincideswith the direction (shown by the arrow B) in which the detection coil 6shown in the diagram is disposed. In this state, when angular velocityaround the axis A is not applied, the vibrator 2 repeats expansion andcontraction in the direction shown by the arrow B and vibratessynchronously with the cycles of the AC voltage included in the drivesignal Sa. Concretely, the vibrator 2 repeatedly deforms its planarshape from the circular shape to an almost oval shape or from the almostoval shape to the circular shape, and oscillates in the direction ofexpansion and contraction by using the first plane PL1 as a reference(center) (in FIGS. 3 to 5, deformation of the vibrator 2 is exaggerated,the state in which the vibrator 2 is deformed in an oval shape isindicated by the alternate long and short dash line, and a state inwhich the vibrator 2 is reset to the circular shape is indicated by thesolid line). In this state, the direction of the combined magnetic fieldC becomes parallel with the detection coil 6, so that the magnetic fluxhardly passes through the inside of the detection coil 6. Therefore, avoltage generated by the combined magnetic field C is hardly induced bythe detection coil 6. For easier understanding, the vibration direction(the direction shown by the arrow B) of the vibrator 2 in this statewill be also called a basic vibration direction.

As shown in FIG. 4, in the case where the angular velocity in theclockwise direction (the direction of the arrow F in the diagram) aroundthe axis A as a center is applied to the angular velocity sensor 1,Coriolis force of the magnitude according to the angular velocity isgenerated in the direction orthogonal to a basic vibration direction Bin the vibrator 2, so that the vibration direction of the vibrator 2changes from the basic vibration direction B to the vibration directionshown by the arrow D in the diagram. In this case, the deviation amountbetween the basic vibration direction B and the direction shown by thearrow D changes according to magnitude of the angular velocity.Similarly, the direction of the magnetic field (magnetic flux) passingthrough the inside of the vibrator 2 also changes (shifts) according tomagnitude of the angular velocity in the same direction of the arrow D.Consequently, the magnetic flux passed in parallel with the wire of thedetection coil 6 at the time of the basic vibration changes so as tocross the wire. As a result, the signal Sc according to magnitude of theangular velocity is induced at both ends of the coil 6. Therefore, thevoltage value of the DC detection voltage Vd generated by thesynchronous detector 7 also changes according to the angular velocity.

On the other hand, as shown in FIG. 5, in the case where the angularvelocity in the counterclockwise direction (the direction of the arrow Gin the diagram) around the axis A as a center is applied to the angularvelocity sensor 1, the Coriolis force according to the angular velocityis generated in the vibrator 2 as described above, and the vibrationdirection of the vibrator 2 changes from the basic vibration direction Bto the vibration direction shown by the arrow E in the diagram. In thiscase as well, the deviation amount between the basic vibration directionB and the direction of vibration indicated by the arrow E changesaccording to magnitude of the angular velocity. Similarly, the directionof the magnetic field (magnetic flux) passing through the inside of thevibrator 2 also changes (shifts) according to the angular velocity inthe direction same as the arrow E. Consequently, the magnetic fluxpassing in parallel with the wire of the detection coil 6 at the time ofthe basic vibration changes so as to cross the wire. As a result, thesignal Sc according to the angular velocity is induced at both ends ofthe coil 6. In this case, the polarity (phase) of the signal Sc becomesopposite (reverse phase) to that in the case where clockwise angularvelocity is applied around the axis A as a center to the angularvelocity sensor 1. Therefore, the voltage value of the DC detectionvoltage Vd generated by the synchronous detector 7 changes according tothe angular velocity similarly except that the polarity (positive ornegative) becomes opposite to that in the case where the clockwiseangular velocity is applied around the axis A as a center to the angularvelocity sensor 1.

Thus, by using the angular velocity sensor 1, the direction (clockwiseor counterclockwise direction) of angular velocity applied to theangular velocity sensor 1 can be specified on the basis of the polarityof the DC detection voltage Vd generated by the synchronous detector 7and, on the basis of the magnitude of the voltage value of the DCdetection voltage Vd, magnitude of the angular velocity can bespecified.

As described above, in the angular velocity sensor 1, the vibrator 2 issupported in a state of no contact with other members including thedetection coil 6 by the supporter 3 fixed to the center portion as thefixed point in expansion/contraction vibrations, and the combinedmagnetic field C is generated in the vibrator 2 by the excitation coil 4to make the vibrator 2 vibrate by making the vibrator 2 expand/contractlike from the circular shape to an almost oval shape and from the ovalshape to the circular shape by using the first plane PL1 passing throughthe center portion (the fixed point supported by the supporter 3) of thevibrator 2, that is, in a vibration state (vibrational mode) whichcannot occur in a normal state. In such a manner, while avoidinginhibition of the vibration of the vibrator 2 by the supporter 3, evenwhen external vibration is transmitted to the vibrator 2, the externalvibration is not transformed to the vibrational mode of the vibrator 2.Consequently, without being influenced by the external vibration, thevibrator 2 can be maintained in a vibration state in the basicvibration. Therefore, the angular velocity sensor 1 can detect angularvelocity with high precision also in a state where external vibration isapplied.

Further, by employing a simple configuration of supporting the vibrator2 by the supporter 3, the angular velocity sensor 1 can be manufacturedat sufficiently low cost. By housing the vibrator 2, excitation coil 4,and detection coil 6 in the case 8 made of a magnetic material, leakageof the magnetic field generated by the excitation coil 4 to the outsideof the case 8 can be prevented, invasion of the external magnetic fieldsto the inside of the case 8 is suppressed, and the influence of theexternal magnetic field onto the vibrator 2 and the detection coil 6 canbe reduced. Since the case 8 configures a closed magnetic path for themagnetic field generated by the excitation coil 4 together with thevibrator 2, leakage magnetic flux can be reduced and, as a result, thevibrator 2 can be vibrated more efficiently.

The present invention is not limited to the foregoing embodiment. Forexample, the example of making the vibrator 2 vibrate by the combinedmagnetic field C generated on the basis of the drive signal Sa obtainedby combining the DC voltage and the AC voltage has been described in theforegoing embodiment. Alternately, the drive signal Sa constructed onlyby the AC voltage without superimposing the DC voltage can be also used.With the configuration, since the DC voltage is not superimposed withthe drive signal Sa, the oscillation driving circuit 5 can be preventedfrom becoming complicated. On the other hand, since no bias magneticfield is applied to the vibrator 2, the efficiency of making thevibrator 2 vibrate deteriorates. However, the oscillation drivingcircuit 5 can be configured simply, so that the angular velocity sensor1 can be configured simply and cheaply. Further, the vibrator 2 can bemade vibrate at a frequency twice as high as that in the configurationin which a bias magnetic field is applied by the DC voltage. Thus, theangular velocity sensor of high vibration frequency can be simplyconfigured.

Although the example of supporting the vibrator 2 by the supporter 3disposed between the center portion of the under face of the vibrator 2and the lower frame of the bobbin 11 has been described in the foregoingembodiment, in place of the configuration, a configuration of supportingthe vibrator 2 (in a suspended state) by the supporter 3 disposedbetween the center portion of the top face of the vibrator 2 and theupper frame of the bobbin 11 can be also employed. Further, aconfiguration of supporting the vibrator 2 from above and from below bydisposing the supporters 3 between the center portion of the under faceof the vibrator 2 and the lower frame of the bobbin 11 and between thecenter portion of the top face of the vibrator 2 and the upper frame ofthe bobbin 11 can be also employed. Further, a configuration in whichone end (lower end) of the supporter 3 is fixed to the lower case 22,thereby directly supporting the vibrator 2 by the lower case 22 via thesupporter 3 in place of the support via the bobbin 11 can be alsoemployed. The case of using the first coil 4 closer to the vibrator 2 asthe excitation coil and using the second coil 6 positioned on theoutside of the first coil 4 as a detection coil in order to efficientlygenerate the magnetic field in the vibrator 2 has been described.Alternately, a configuration of using the first coil 4 as a detectioncoil and using the second coil 6 positioned on the outside of the firstcoil 4 as the excitation coil ca be also employed.

The angular velocity sensor 1 can be used singly. As shown in FIG. 6, athree-axis angular velocity detector 31 can be also configured bycombining three angular velocity sensors 1A, 1B, and 1C. The angularvelocity detector 31 includes the three angular velocity sensors 1A, 1B,and 1C, a fixing member 32, and the oscillation driving circuits 5 andthe synchronous detectors 7 (which are not shown) for the angularvelocity sensors 1A, 1B, and 1C. In this case, the angular velocitysensor 1A is set so that its axis is in parallel with the X axis, theangular velocity sensor 1B is set so that its axis is in parallel withthe Y axis, and the angular velocity sensor 1C is set so that its axisis in parallel with the Z axis. The angular velocity sensors 1A, 1B, and1C are fixed to the fixing member 32. The angular velocity detector 31can detect angular velocity in all of the three axes simultaneously.Although not shown, in the case of detecting the angular velocity addedto an object which moves only in a predetermined plane, for example, atwo-axis angular velocity detector can be also configured by the twoangular velocity sensors 1A and 1B without using the angular velocitysensor 1C disposed in the Z axis in the diagram.

Obviously, the angular velocity sensor 1 and the angular velocitydetector can be applied not only to a camera-shake correcting mechanism(unsteadiness correcting mechanism) employed for a video camera or thelike but also to a navigation system and an attitude controller of acar, an airplane, or the like.

1. An angular velocity sensor comprising: a vibrator made of amagnetostrictive material in a disc shape in plan view; a first coildisposed along a first plane which includes an axis of the vibrator, thefirst coil enclosing the vibrator; a supporter supporting the vibratorat a position where the axis crosses the surface of the vibrator, thesupporter made of a nonmagnetic material; and a second coil disposedalong a second plane which crosses the first plane and includes theaxis, the second coil enclosing the vibrator and the first coil, whereinone of the first and second coils generates a magnetic field in thevibrator on the basis of an excitation current supplied, thereby makingthe vibrator vibrate in the direction of the magnetic field, and theother one of the first and second coils detects a magnetic flux changecaused by a change in the vibration of the vibrator, the change in thevibration occurring depending on angular velocity.
 2. The angularvelocity sensor according to claim 1, further comprising a case made ofa magnetic material for housing the vibrator, the first coil, and thesecond coil.
 3. An angular velocity detector configured by disposing anangular velocity sensor on each of two axes which are orthogonal to eachother, wherein each of the angular velocity sensors comprises: avibrator made of a magnetostrictive material in a disc shape in planview; a first coil disposed along a first plane which includes an axisof the vibrator, the first coil enclosing the vibrator; a supportersupporting the vibrator at a position where the axis crosses the surfaceof the vibrator, the supporter made of a nonmagnetic material; and asecond coil disposed along a second plane which crosses the first planeand includes the axis, the second coil enclosing the vibrator and thefirst coil, wherein one of the first and second coils generates amagnetic field in the vibrator on the basis of an excitation currentsupplied, thereby making the vibrator vibrate in the direction of themagnetic field, and the other one of the first and second coils detectsa magnetic flux change caused by a change in the vibration of thevibrator, the change in the vibration occurring depending on angularvelocity.
 4. An angular velocity detector configured by disposing anangular velocity sensor on each of three axes which are orthogonal toeach other, wherein each of the angular velocity sensors comprises: avibrator made of a magnetostrictive material in a disc shape in planview; a first coil disposed along a first plane which includes an axisof the vibrator, the first coil enclosing the vibrator; a supportersupporting the vibrator at a position where the axis crosses the surfaceof the vibrator, the supporter made of a nonmagnetic material; and asecond coil disposed along a second plane which crosses the first planeand includes the axis, the second coil enclosing the vibrator and thefirst coil, wherein one of the first and second coils generates amagnetic field in the vibrator on the basis of an excitation currentsupplied, thereby making the vibrator vibrate in the direction of themagnetic field, and the other one of the first and second coils detectsa magnetic flux change caused by a change in the vibration of thevibrator, the change in the vibration occurring depending on angularvelocity.